In the oil and gas exploration and production industry, wellbores are drilled in order to access subsurface hydrocarbon-bearing formations. The viability of a well may vary in response to many factors. For example, in some instances the costs involved in producing hydrocarbons from a well may not justify its continued operation. This may be the case, for example, with a mature well where the most accessible hydrocarbons have been extracted and the costs associated with extracting the remaining hydrocarbons is or becomes prohibitive. Alternatively, in a well where the hydrocarbons are more readily accessible, the market cost of the produced hydrocarbons may dictate that the continued operation of the well is not commercially viable. In other instances, the wellbore may be abandoned due to technical issues.
Where it is desired to close a well, it is necessary to do so in a manner which prevents the escape of any hydrocarbons to the surrounding environment. The process may involve, amongst other things, the insertion of fluid, such as drilling mud, to kill the flow of hydrocarbons to surface, the introduction of cement into the wellbore to isolate hydrocarbon reservoirs from each other or from surface, or the removal of bore-lining tubing or other equipment located at surface or on the seabed. The well may then be capped, for example by locating a wellhead on the well.
It will be recognised that the closure of a well is a complex and expensive procedure, in particular in the case of subsea wells or wells in other remote locations.
There are, however, a number of situations where it may be desired to regain access to the well. For example, advances in technology may make the previously inaccessible or uneconomical extraction of hydrocarbons viable. Alternatively, market value of the extracted hydrocarbons may increase to a point where the extraction of hydrocarbons from the well becomes commercially viable.
However, re-opening of an abandoned or closed well is technically challenging and expensive, and may not be feasible in many instances if indeed it is possible using conventional techniques and equipment.